code: def test_prefixsum_idx2(self):
      tree = SumSegmentTree(4)
  
      tree[0] = 0.5
      tree[1] = 1.0
      tree[2] = 1.0
      tree[3] = 3.0
  
      assert tree.find_prefixsum_idx(0.00) == 0
      assert tree.find_prefixsum_idx(0.55) == 1
      assert tree.find_prefixsum_idx(0.99) == 1
      assert tree.find_prefixsum_idx(1.51) == 2
      assert tree.find_prefixsum_idx(3.00) == 3
      assert tree.find_prefixsum_idx(5.50) == 3
  
file_path: ray/rllib/utils/replay_buffers/tests/test_segment_tree_replay_buffer_api.py
imports: import numpy
  import unittest
  from ray.rllib.execution.segment_tree import SumSegmentTree, MinSegmentTree
label_desc: Use image node_id 4 for calling the TestSegmentTree obj's underlying member method code with example usage: obj.test_prefixsum_idx2() without return types